Lexington Weather

Lexington, Massachusetts, USA

66°F

5/20/2024 3:51pm

Lexington Conditions: Clear
Temperature: 66.0°F / 18.9°C
Dew Point: 57.2°F
Relative Humidity: 73%
Wind: Calm, 10-min avg: Calm, gust: None
Barometer: 29.98 in Steady
Visibility: 10 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 171839
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
239 PM EDT Fri May 17 2024

.SYNOPSIS...

Mild across the interior today but increasing clouds and onshore 
winds will keep temperatures cool across eastern MA and RI. 
Seasonable with light rain/drizzle on Saturday. We are then 
looking at a prolonged spell of dry weather with warming 
temperatures starting Sunday and continuing through Wednesday. 
High temperatures could approach the mid 80s by Tuesday and/or 
Wednesday in interior Southern New England, with temperatures in
the 70s near the coasts. Our next chance for rains doesn't 
appear until around Thursday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

230 PM Update...

Forecast remains on track. Have just brought things in line with
latest obs.

705 AM Update:

Cloud cover this morning is something of a mixed bag. Most 
persistent overcast continues along the southern roughly third 
of Southern New England, from northern Hartford County eastward 
through central Bristol County in MA and into South Shore. 
However, we've seen returning shallow moisture on NNE/ENE flow
into eastern and east-central MA. This latter area of clouds
seems best handled by the RAP model RH profiles, and indicates
this layer of moisture is a lot more shallow than the more
concentrated cloud layer in CT-RI and portions of SE MA. So we
think the cloud cover in eastern MA should scatter or lift out
by mid to late morning as heating gets going, but will take a
little while longer the further south one goes. Will see
increasing NE breezes today too. All in all, variable amounts of
cloud cover but should trend partly to mostly sunny near and
north of the Mass Pike, with overcast during the morning to
early afternoon along the south coast, but we should see some
breaks in cloud cover even if those locations don't go fully 
clear. No changes to highs which still look on track.

Previous discussion:

Portions of far southern New England remain under the northern 
fringes of the stratus deck associated with low pressure well 
south of the region this morning which has allowed light rain 
showers to filter over the Cape and Islands over the last 
several hours. In contrast, the interior, mainly north of the 
Providence to Hartford line has been persistently clear, thus, 
radiation fog has been able to form in locations where dewpoints
have dropped below ~50F (Fitchburg, Orange, BAF Airfield). The 
expectation for today is that low pressure will continue to 
drift south as mid level ridging nudges in from the southwest, 
allowing for a period of sunshine this morning north and west of
the I-95 corridor. Areas that are able to capitalize on a few 
hours of sunshine will be able to mix to ~850mb where temps 
hover around 8C. 

Cloud cover and wind direction will have a significant influence on 
temperatures today, with 925mb jet holding strong over SE MA and RI, 
where winds will continue to gust to as high as 20kt this afternoon 
from the NE. So, while places in the Connecticut River Valley will 
warm quickly into the 70s, a significant temperature gradient will 
develop with areas east of approx. Worcester warming into the mid 
60s this morning before synoptic flow drops temperatures into the 
low 60s and 50s along the immediate coastline late this afternoon. 
This, "synoptic seabreeze" may extend as far inland as the I-495 
corridor prior to sunset. Onshore flow will also influence the 
development of afternoon cloudiness.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...

Weak shortwave will rotate around a low centered over northern 
Quebec/Ontario on Saturday as low pressure south of the region 
pivots ever so slightly north back towards SNE. The combined 
influence of the shortwave as well as some convergence from onshore 
flow will result in scattered shower activity very late tonight 
through the day on Saturday. Showers will be most widespread across 
eastern MA and RI but even so, not expecting a washout of a day. The 
NAM is the most bullish of guidance hinting at the potential for up 
to an inch and a half of rain to fall across far northeastern MA 
over the period ending 00Z Sunday, but a check of the 24 QPF HREF 
PMM paints a much more moderate solution with localized max QPF of 
around a half of an inch in Essex and northern Middlesex counties. 

The temperature forecast is proving to be quite tricky for Saturday, 
with the wetter, cloudier guidance, such as the NAM, really leaning 
into onshore flow to drive highs down into the mid to upper 50s 
region wide! In contrast to the NAM, most other guidance depicts 
widespread highs in the 60s away from the immediate coastline. Given 
the high level of uncertainty regarding temps tomorrow afternoon, 
relied heavily on "consensus" guidance to derive high temperatures. 
With widespread cloudiness, mixing will be limited, but should some 
portions of the CT River Valley be able to break out into brief 
period of sunshine, could see temps warm into the upper 60s in 
places like downtown Hartford and Windsor Locks.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...

Highlights: 

* Significant warmup toward late-spring/early-summerlike 
  temperatures as we move into the early to midweek period. Likely 
  to see Tue and Wed reach into the lower to mid 80s inland! 

* Outside of diminishing spotty showers early Saturday evening, 
  mainly dry weather is expected with high pressure dominating.

Details:

Though we could still be dealing with hit or miss showers over 
eastern and northeast MA early Saturday evening, the forecast 
continues to trend more optimistically with decreasing cloudiness 
starting on Sunday. Expect cooler temps again near the coasts as 
onshore flow continues, with highs in the lower to mid 60s; while 
further inland, highs should push well into the 60s to the lower/mid 
70s. 

The main story for the early to midweek portion of the forecast is a 
warming trend toward late-spring/early-summerlike temperatures 
accompanied by dry weather, as 500 mb heights rise over Southern New 
England. 850 mb temps will also be steadily rising to values around 
+11 to +13C by Tuesday, and around +12 to +14 C by Wednesday. Warmup 
begins in earnest on Monday, with highs reaching into the 70s with 
perhaps a spot 80 degree reading in the CT and Merrimack Valleys. 
Some concern for cooling seabreezes near the immediate coast and 
kept temps for both coasts in the mid 60s to around 70. Warmest days 
in the stretch look to be both Tuesday and Wednesday with high 
pressure to our south promoting a strengthening SW pressure 
gradient. Several days of antecedent dry weather would also tend to 
favor warmer temps. That would keep the sea breeze from making any 
landward inroads and allow for warm temperatures to make it all the 
way to the eastern coast with little resistance. Outside of Cape Cod 
where highs still only around the mid to upper 60s, temps on Tuesday 
and Wednesday should soar well into the 70s for most, with lower to 
mid 80s in the CT/Merrimack Valleys.  

This period is overall a dry one outside of spotty rain showers 
early Saturday evening. We may not see our next chance for rains 
until around Thursday as a cold front approaches from the west, but 
this is by no means set in stone.

&&

.AVIATION /19Z FRIDAY THROUGH TUESDAY/...

Forecast Confidence Levels:

Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent. 

Through 00Z...High confidence away from the Cape/Islands where
confidence is moderate. 

VFR for most with NE winds 10-20 kts. Should see some 20-30 kt
gusts with the highest speeds/gusts across the Cape and Islands.
Will gradually see MVFR to IFR and perhaps even some localized
LIFR stratus lifting toward the Cape/Islands as we head toward
00Z. Could have some spotty rain/drizzle with this deck as well.

Tonight... Moderate confidence

VFR to start away from the Cape/Islands where MVFR/IFR
conditions persist. Will see this MVFR/IFR stratus spread
northwestward as the night progresses. Though think IFR with
localized LIFR remains generally ORH-BVY-WST eastward. Will have
spotty rain/drizzle with this stratus. Persistent NE flow at
5-15 kts. Could see some gusts of 20-25 kts across the
Cape/Islands.

Saturday...Moderate confidence.

MVFR to IFR conditions persisting with localized LIFR across the
Cape/Islands. Think that the CT River Valley could break out to
VFR toward 18Z. Will have persistent NE winds at 5-15 kts with a
few gusts up to 20 kts along the immediate east coast. Spotty
rain/drizzle throughout the day.

Saturday Night...Moderate confidence.

MVFR to IFR conditions persist due to pesky onshore flow. Could
also have some spotty localized LIFR condition. Light rain and
drizzle continues with the best shot along the immediate
coastline. Winds NNE to NE at 5-15 kts with a few gusts up to 20
kts toward daybreak along the Cape/Islands.

KBOS TAF...High confidence in TAF through 00Z. Moderate after
this time.

VFR with NE winds at 10-15 kts through roughly 02Z. Will see
ceilings lowering to MVFR/IFR tonight with drizzle/rain
spreading in toward 03-06Z. Light rain/drizzle persistent
through Sat with NE winds and IFR conditions. 

KBDL TAF...High confidence in TAF. 

VFR this afternoon and this evening. Could see some borderline
MVFR ceilings spread in late tonight, but better shot comes Sat
AM and persists through the afternoon. Could see some spotty
rain/drizzle on Sat.

Outlook /Sunday through Tuesday/...

Sunday: Mainly VFR, with local MVFR possible. Breezy. 

Sunday Night through Tuesday: VFR. 

&&

.MARINE...

Forecaster Confidence Levels:

Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent. 

3AM Update... Extended SCA for outer waters through 00-06Z
Sunday 

Today... High Confidence.

Any pockets of fog burning off by mid to late Fri AM. E/ENE 
winds 15-20 kt with 20-25 kt gusts. Seas remain elevated across
the outer waters, so the SCA remains.

Tonight...High confidence.

Winds remain out of the NE at 10-20 kts. Could see a return of
stratus/fog across the waters late. Visibilities of 1-4 SM with
the lowest across the eastern waters. Seas remain elevated so
have extended the SCA through the period.

Saturday... High Confidence

Scattered showers with persistent E/NE flow. Gusts to around
15kt. Seas gradually subsiding but remain above 5ft across the
outer waters, thus, extended SCA through Saturday evening. 

Outlook /Saturday Night through Tuesday/...

Saturday: Winds less than 25 kt. Areas of rough seas. Chance of
rain, patchy fog. Local visibility 1 to 3 nm.

Saturday Night: Winds less than 25 kt. Seas up to 5 ft. Slight
chance of rain, patchy fog. 

Sunday through Monday: Winds less than 25 kt. Seas up to 5 ft. 

Monday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. 

Tuesday: Winds less than 25 kt. Seas locally approaching 5 ft. 

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 2 AM EDT Sunday for ANZ250-254.
     Small Craft Advisory until 8 PM EDT Saturday for ANZ255-256.

&&

$$

SYNOPSIS...Loconto/KS
NEAR TERM...Loconto/BL/KS
SHORT TERM...KS
LONG TERM...Loconto
AVIATION...BL
MARINE...Loconto/KS